Furfural is an industrially useful chemical. Conventionally, furfural can be produced from C5 sugars which have been obtained from hydrolysis of the hemicellulose contained in biomass. Typically, the hydrolysis of biomass is performed with aqueous acids at relatively high temperatures to obtain C5 and C6 sugars derived from xylan and glucan, respectively. Any furfural generated, when left in the monophasic aqueous reaction mixture of sugars, can undergo degradation via condensation initiated by reactive sugar intermediates. Besides resulting in lower yield of the desired furfural product, costly separation steps to isolate the furfural from other intermediates is needed. Such separation step(s) can increase process complexity as well.
U.S. Pat. No. 4,154,744 relates to an improved process for producing a furan derivative having the formula shown below
wherein R is hydrogen, methyl, or chloromethyl, which comprises reacting a monosaccharide or a disaccharide with hydrochloric acid in a mixture containing water, an organic solvent and a catalytic amount of a surface active agent.
U.S. Pat. No. 4,533,743 discloses that furfural yield and selectivity are maximized by reacting a 1 to 10 percent pentose 0.05 to 0.2 normal mineral acid aqueous solution in a plug flow reactor operated at a temperature between 220° C. and 300° C. Two preferred arrangements are disclosed: a single phase, pentose recycle operation in which the furfural is recovered by solvent extraction and distillation, and a two phase, solvent recycle operation in which solvent is added to the reactor and furfural is recovered from the solvent by distillation.
United States Patent Application Publication No. 2008/0033188 relates to a process to make furan derivative compounds. The process comprises dehydrating a carbohydrate feedstock solution, optionally in the presence of an acid catalyst, in a reaction vessel containing a biphasic reaction medium comprising an aqueous reaction solution and a substantially immiscible organic extraction solution. The aqueous reaction solution, the organic extraction solution, or both the aqueous reaction solution and the organic extraction solution, contain at least one modifier to improve selectivity of the process to yield furan derivative compounds in general, and 5-hydroxymethyl-2-furfural (HMF) in particular.
Processes for obtaining furfural in high purity and selectivity from biomass continue to be sought. In particular, processes are desired in which lignocellulosic biomass comprising both glucan and xylan can be used as feedstock to provide furfural selectively and in good purity, relatively free of HMF. Also desired are processes in which the separation of furfural from HMF is simplified.